A Multi Chassis Port Channel (MCPC) or Multi Chassis Ether Channel (MCEC) has two ends of a port channel termination on two different switches. These switches are commonly referred to as Aggregation Switches. Having multiple ends of a port channel terminate on different channels provides redundancy, not only across link failure, but also across a single switch failure.
In contrast, in a regular Port Channel, all links belonging to the Port Channel terminate on a single switch. The Port Channel is treated as a single logical link by Spanning Tree Protocol (STP), and any hardware operations like setting the port state or MAC flush/Age are applied on all member links of the Port Channel. As such, STP does not pose any issues on a regular Port Channel.
However, operating STP on an MCPC complex presents some challenges, as member links of the Port Channel are terminating on different switches. One of these challenges is that STP may block a port used to establish a multi-channel trunk (MCT) between MCPC switches. If an MCT port is blocked, the desirable redundancy offered by an MCPC topology may be lost.
Overview
One embodiment provides a method. The method generally includes maintaining a multi-chassis port channel (MCPC) priority vector for a port of a switch of an MCPC complex, wherein the MCPC priority vector includes a field whose value is determined based on whether or not the port is used to establish a multi-chassis trunk (MCT) in the MCPC and performing spanning tree protocol operations, based on the MCPC priority vector, to determine whether or not to allow forwarding on the port.
One embodiment provides a switching device. The switching device generally includes a first port for establishing a multi-chassis trunk (MCT) with another switching device for use in multi-chassis port channel (MCPC) communications, at least a second port for communicating with a device external to the MCPC, logic for maintaining a multi-chassis port channel (MCPC) priority vector for a port of a switch of an MCPC complex, wherein the MCPC priority vector includes a field whose value is determined based on whether or not the port is used to establish a multi-chassis trunk (MCT) in the MCPC, and logic for performing spanning tree protocol operations, based on the MCPC priority vector, to determine whether or not to allow forwarding on the port.
One embodiment provides a switching device. The switching device generally includes at least a first port for establishing a multi-chassis trunk (MCT) with another switching device for use in multi-chassis port channel (MCPC) communications, at least a second port for communicating with a device external to the MCPC, means for maintaining a multi-chassis port channel (MCPC) priority vector for a port of a switch of an MCPC complex, wherein the MCPC priority vector includes a field whose value is determined based on whether or not the port is used to establish a multi-chassis trunk (MCT) in the MCPC, and means for performing spanning tree protocol operations, based on the MCPC priority vector, to determine whether or not to allow forwarding on the port.